Artificial satellites have traditionally been relatively large-scale devices deployed in orbits about the earth for observation of the earth's surface, or carrying directive antennas for use as communications repeaters. Such satellites must be oriented with respect to the earth to function effectively. Previously proposed satellite orientation techniques have relied upon reaction jets, or rotating fly-wheels, to rotate the satellite into the desired orientation in response to a sensing device as the satellite orbits the earth. Sensing devices have included electromagnetic radiation sensitive devices for sensing the position of the horizon circle of the earth as seen from the satellite, gyroscopic devices for determining the gravity vertical of the earth, sun sensors, horizon sensors, and star trackers. However, the effective life of reaction jet orientation systems is limited by the amount of jet fuel carried aboard the satellite, as well as by the rate of expenditure of fuel required by stabilization of satellite perturbations. Fly-wheel arrangements are inherently heavy, consume a great deal of the limited power available aboard a satellite that is oriented by applying torque to revolve an internal wheel, and provide a failure point with the use of bearings.
More recently, smaller, single use satellites have been contemplated. However, as the size of satellites are reduced, it becomes more difficult to scale down the size and power/fuel consumption of devices used to orient the satellite or keep the satellite oriented.